LITIGATION ON GRAVITY PIPE FAILURES IMMINENT - NORTH AMERICAN EXPERT:
Article Date: 11 May 2007
Gerry Mulhern, vice president of the North American company, Hanson Pipe and Products Precast, and a world authority on various types of gravity piping, says that South Africa could well follow North America’s example in suing municipal and other engineers for trenched gravity pipe failures.
Mulhern says most engineers and contractors in North America don’t understand the differences between a rigid concrete pipe and a flexible pipe and that the potential for trenched gravity pipe failure has increased substantially with the introduction of plastic piping.
“The USA and Canada are very litigious societies and professionals are being sued for pipe failures. The same could well happen in South Africa, especially within the framework of the Occupational Safety Health Act (OSH ACT).
“South Africa appears to have the legislation in place but in many instances it is not being adhered to.
“One of the ways of safeguarding against failure of flexible pipes and subsequent litigation is the simple deflection test. However, almost all the delegates who have attended my South African seminars said that deflection testing did not form part of their flexible pipe trenching specifications. Municipal engineers who don’t specify some form of deflection testing on flexible piping are operating on a wing and a prayer, hoping the contractor is going to do the job properly.
“Both Mandrel and infra-red testing force the contractor to lay pipes properly. Mandrels are very simple to use and are deployed widely across North America. Laser technology is newer and is also available in South Africa.
“Deflection testing is especially important for PVC, HDPE and GRP (flexible) piping because 95% of a flexible pipe’s strength is derived from the surrounding or imported soil. Should deflection exceed 5% then the pipe has not been installed properly. Obviously, the higher the deflection rate the shorter the service life of the piping.”
Mulhern has also cautioned engineers on the use of different types of piping joints because, as he observes, this is where failure is most likely to occur, especially when two types of materials are joined.
“Engineers need to educate themselves on PVC, HDPE and GRP joints because all flexible pipes are designed to deflect.
“Take an example where two flexible pipes are joined together. If the one pipe deflects 3% and the other 5%, one has a 2% differential. Assuming that the piping has a diameter of 1 800mm then the differential is 36mm. This will let a lot of water escape unless the joint has the capacity to take up that kind of differential.
“I am surprised that there are no flexible water-tight couplings for joining flexible piping to manholes in this country. In the USA they have existed for many years and there is certainly a need and a commercial opportunity for them in the Republic. Grouting is the correct procedure for connecting concrete piping into manholes, however, grouting flexible pipes into concrete manholes, as is done in SA, sooner or later results in failure through deflection.
“A flexible manhole coupling is required to take up that deflection. The problem with grouting flexible piping into manholes is that when deflection does occur the grouting cracks and breaks up. This represents a potentially huge area for future pipe failure in SA,” observes Mulhern.
He says one of the major difficulties in installing flexible pipes is adhering to safety standards and regulations such as the OSH ACT while simultaneously following installation specifications.
“One or the other is generally compromised. As a reinforced structure with built-in strength, concrete is far less dependent on embedment material than flexible piping. Because of its rigid nature, contractors don’t incur the same sort of difficulties with concrete piping as they do with the proper installation of flexible pipe products. These difficulties become even more pronounced when working in trenches.”
Mulhern said that despite the fact that plastic piping is supposed to have a lifespan of up to 50 years, problems and pipe failure are already apparent after comparatively short lifespans.
“Litigation on pipe failure in the US involves not only what one does, but what one fails to do, and I suspect the same applies or will apply in South Africa. The main point here is that one must make the right decision with the host pipe. If not, the consequences both in terms of expense and ruined reputations can be punitive.
“For anyone seeking value for your money and peace of mind, concrete is the route to go. South Africa can’t afford reworks,” concludes Mulhern.”
Mulhern has visited South Africa twice over the past four years as the guest of the Concrete Manufacturers Association (CMA). While here he held seminars on infrastructural piping for civil and municipal engineers as well contractors. A leading authority on gravity pipe products, he has wide ranging expertise on several different types of infrastructural piping including corrugated metal, HDPE, and concrete.
Gerry Mulhern (left) vice president of the North American company, Hanson Pipe and Precast and Danie Greeff, vice president of the CMA P.I.P.E.S Division demonstrate a point at a pipes seminar held in Midrand last year.
Interlocking concrete pipes, 1 650mm in diameter, are offloaded for installation in a main storm water pipeline in Pretoria.
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